The invention relates to a device for indirect extrusion of a hollow section from a billet, in particular a hollow aluminum billet which is presented to a shape-giving opening of a die by an extrusion stem, the die being such that a billet container can be moved over it, thus enclosing it, and a mandrel which determines the inner contour of the hollow section is provided in the shape-giving opening of the die.
When hot forming a billet, pre-heated to the extrusion temperature, to strands or rods, the billet which is enclosed in the container is usually pressed by the extrusion stem of a hydraulic extrusion press into the stationary shaping die; the stem or a so-called dummy block on the extrusion stem forms the backing for the material which is to be extruded.
When extruding by the so-called indirect extrusion method, either the shaping tool, the die, is pushed into the stationary container or the latter is moveable and can be pushed over the die thus enclosing it. In both cases, prior to extrusion, a new billet is placed in the container next to the backing and compressed to fill the space around it in the container.
The die is mounted on a long tool stem which is subjected to high thermal and mechanical stresses; this tool stem must be hollow as the strand formed has to pass through it. By supporting the die the whole of the extrusion force acts on the tool stem during the extrusion stroke, this usually includes, besides the purely compressive forces, also torsional and bending forces. Furthermore, the mandrel projects into the tool stem.
Applications exist for hollow sections in the form of seamless, hollow tubes featuring flanges at the end joined to the tube body with as little change in structure as possible. Such an application, for example, is to be found in containers used in uranium precipitation plants; these containers usually comprise a hollow tube body with a flange welded onto and machined at one end.